The present invention relates, in general, to the field of magnetic recording heads. More particularly, the present invention relates to a technique for reducing pole tip protrusion (“PTP”) in a magnetic write head and giant magnetoresistive (“GMR”) stripe temperature in an associated read head structure utilizing one or more internal diffuser regions.
Recording heads are miniature components (with dimensions of on the order of about 1 mm2) that read and write information to and from a hard-drive disk or another storage medium. When writing, the head acts as a small electromagnet wherein positive and negative pulses of current are translated into north and south magnetic poles on a rotating magnetic disk. When reading, the head senses magnetic fields from these poles and translates the alternating fields into positive and negative voltage pulses. These pulses become the bits of digital information stored on the disk. A recording head is generally bonded or otherwise affixed to a metal suspension, which is a small arm that holds the head in position above or beneath a rotating disk. The head and suspension is sometimes referred to as a head-gimbal assembly or HGA. Sets of HGA's stacked together for installation in a disk drive are denominated a head-stack assembly or HSA.
In general, recording heads function according to certain principles of magnetic recording which are based directly on four magnetic phenomena. These are: a) an electric current produces an accompanying magnetic field; b) Soft magnetic materials are easily magnetized when placed in a weak magnetic field and, when the field is turned off, the material rapidly demagnetizes; c) In some magnetically soft materials the electrical resistance changes when the material is magnetized and this resistance returns to its original value when the magnetizing field is turned off. This is the magnetoresistive (“MR”) effect. The larger giant magnetoresistive (“GMR”) effect, is exhibited by specific thin film materials systems; and d) Certain other materials are magnetized only with relatively greater difficulty (i.e., they require a strong magnetic field), but once magnetized, they retain their magnetization when the field is turned off. These are called hard magnetic materials or permanent magnets.
With respect to data storage, heads used for writing bits of information onto a spinning magnetic disk depend on phenomena a) and b) to produce and control strong magnetic fields. Reading heads depend on phenomena a), b), and c), and are sensitive to the residual magnetic fields of magnetized storage media d). On the other hand, magnetic storage media are permanently magnetized in a direction (North or South) determined by the writing field. Storage media exploit phenomenon d).
In the writing of data, a spiral coil is wrapped between two layers of soft magnetic material and at the lower end, there is a gap between these layers. At their upper end, these layers are joined together. The top and bottom layers of magnetic material are readily magnetized when an electric current flows in the spiral coil, so these layers become effectively the “North” and “South” magnetic poles of a small electromagnet. [In an actual head, the distance from the gap to the top of the coil may be on the order of about 30 microns (or 0.0012 inch).] The North-South poles at the gap end of the writing head further concentrate the field at this point, which is the area where the writing field leaks into space outside the head. When a magnetic storage medium (a spinning computer disk, for example) is placed in close proximity to the writing head, the hard magnetic material on the disk surface is permanently magnetized (or written) with a polarity that matches the writing field. If the polarity of the electric current is reversed, the magnetic polarity at the gap also reverses.
Computers store data on a rotating disk in the form of binary digits, or bits, transmitted to the disk drive in a corresponding time sequence of binary one and zero digits, or bits. These bits are converted into an electric current waveform that is delivered by wires to the writing head coil. In its simplest form, a “one” bit corresponds to a change in current polarity, while a “zero” bit corresponds to no change in polarity of the writing current. A moving disk is thus magnetized in the positive (North) direction for positive current and is magnetized in the negative (South) direction for negative current flow. In other words, the stored “ones” show up where reversals in magnetic direction occur on the disk and the “zeroes” reside between the “ones”.
A timing clock is synchronized to the rotation of the disk and bit cells exist for each tick of the clock. Some of these bit cells will represent a “one” (a reversal in magnetic direction such as North going to South or South going to North) and others represent “zeroes” (constant North or constant South polarity). Once written, the bits at the disk surface are permanently magnetized in one direction or the other until new data patterns are written over the old. A fairly strong magnetic field exists directly over the location of “ones” and fades rapidly in strength as the recording head moves away. Moving significantly in any direction away from a “one” causes a dramatic loss of magnetic field strength. Thus, to reliably detect data bits, it is extremely important for reading heads to fly very close to the surface of a magnetized disk.
A basic writing head generally comprises a magnetic yoke, a writing gap in the yoke, and a coil for energizing the head field. Conventional reading heads have a GMR element with excitation/sensing leads and magnetic shield layers on both sides of the sensor. While writing and reading are clearly independent functions, it is very important to place write and read heads in close proximity to the recording medium, both to have the write gap and GMR element close to each other as well as to maintain tight geometrical alignment between both heads. In this manner, the top shield of the GMR sensor becomes the bottom magnetic pole of the writing head and the result is an integrated write-read structure, or so-called “merged-head” or “shared shield” design, where the GMR head and writing head share a common magnetic layer. (c.f. http://www.readrite.com)
Conventional inductive transducers for reading and writing information to magnetic storage media comprise layers of differing materials stacked together to enable them to effectuate their specified magnetic and mechanical functions. Relatively hard materials, such as ceramics, may be used for the head substrates while relatively softer magnetic poles and insulating layers are also required for their inherent magnetic and electrical properties. In use, the differential wear properties of these materials can cause the pole pieces to effectively recede from the air bearing surface (“ABS”) resulting in what is known as pole tip recession (“PTR”). This undesired phenomena causes an increased spacing of the write head from the storage media with a concomitant and undesired decrease in available write density.
At the same time, these transducers can also exhibit pole tip protrusion (“PTP”) problems due to the differing thermal expansion coefficients of the various layers as well as high GMR temperature problems due to excessive heat generated in the head structure from the electric current applied to the coils of the write head.